Permanent hair colorants commonly come in two parts: a dye solution and a developer solution. In a conventional permanent hair coloring treatment, the dye solution and the developer solution are mixed and then immediately applied to the hair. After a time interval of about 25 to about 45 minutes, the hair is rinsed with water, treated with a post treatment conditioner, and then rinsed again with water.
The application of the dye solution and the developer solution affords permanent hair coloring. However, use of this conventional method does not provide maximum color deposition or retention and the range of color nuances especially in the red shades is limited.
The duration over which dyed hair remains colored is in principle only limited by the hair growth rate assuming the treatment does not affect the color of the hair as it is formed, i.e., “roots”. In practice dye films deposited on the hair are susceptible to extraction by repeated shampooing, erosion by combing and brushing, and fading by exposure to sunlight and oxygen. Red colors are particularly susceptible to these degrading processes and in an attempt to achieve sufficiently deep and long lasting red shades consumers often try to compensate by increasing the intensity of the initial color. However, this can lead to hair that has an unnatural or painted appearance.
The underlying problem in achieving natural, long-lasting colors through oxidative dyeing is that only a small portion of the color enters the interior of the hair fiber during the dyeing process. As is well known, the color of oxidative dyes arises from the oxidative coupling of primary intermediates and secondary intermediate (often called couplers)—essentially dimerization and/or polymerization. Thus, oxidative coupling leads to an increase in molecular weight as well as an increase in conjugation. However, as the molecular weight rises, it becomes increasingly difficult for the polymerized dye to penetrate the hair fibers. Thus, the darkest colors are more likely to remain at the surface of the hair fibers where they are most susceptible to erosion, and abrasion. Being on the outside of the fibers these colors are also in an “optical environment” that is least similar to the environment of the natural melanins in hair, i.e., dispersed within the hair fiber matrix. The term “painted” often used to describe the unnatural appearance of darkly dyed hair is more than coincidental!
It has been shown in U.S. Patent Publication 2003/0154562, incorporated herein by reference, that a two step method wherein the oxidative dye precursors are allowed to contact the hair in a substantially inactive form before the developer is applied to the hair can achieve a much more durable color change. By “more durable” we mean more resistant to repeated shampooing, and abrasion, e.g., brushing. Apparently, the small precursor molecules can diffuse deeper into hair fibers before polymerization takes place to limit their diffusion. Thus, during the first step, the rate of diffusion of the dye is greater than the rate of oxidation.
The current inventors have observed however, that the intensity of color provided by the 2-step process is variable and highly composition dependant. Utilizing the same developer mixture and oxidative dyes, it has been observed for example, that the type and level of ingredients used in the dye precursor mixture, i.e., the mixture that is applied first to the hair, has a major impact on the resulting hair color. Based on an extensive and systematic study of the types and levels of fatty ingredients and organic solvents in the precursor mixture, the inventors have identified compositions that maximize the color change provided by the two step process.
Surprisingly these optimal dye precursor compositions provide benefits to the hair coloring system in addition to stronger color deposition. These additional benefits include: i) conditioning effects which allows facile removal of excess dye precursor mixture prior to the application of the developer mixture; and ii) protection of the hair from damage during the oxidative color development stage of the process
For optimal performance, the dye precursor mixture should include a fatty amine among the fatty ingredients employed in the mixture. Furthermore, the total level of fatty ingredients should be less than a critical value, which is dependent on the total level of organic solvent in the dye precursor composition. This latter criticality can be expressed by a mathematical inequality that is useful in defining the composition space for optimal dye uptake and color intensity.
The following patents and publications have been considered:
U.S. Patent Publication No. 2003/0113286 discloses a hair coloring and conditioning composition having an oxidative dye composition part and an oxidant part that are mixed prior to use. Cationic surfactants are mentioned as conditioning agents.
U.S. Pat. No. 6,379,400 discloses dye compositions that employ a class of direct nitro dyes in a 1-step coloring process. All examples are of compositions that contain anionic surfactants.
U.S. Pat. No. 6,673,122 teaches dyeing compositions containing novel aminophenols intended primarily for 1-step coloring of hair. No distinction is made concerning surfactant type.
U.S. Patent Publication No. 2004/0006832 concerns hair-dyeing compositions containing as coupling agent, selected 3,5 diamino pyridine derivatives. All the exemplary compositions are used in a 1-step hair coloring process.
U.S. Pat. No. 6,613,313 is directed to aniline dyes of specific compositions used for coloring hair in a 1-step process.
U.S. Patent Publication No. 2003/0163877 concerns a rinse-off coloring composition including clay and an agent imparting color to hair. No oxidative dyes are used and consequently there is no mention of the penetration of such dyes into the hair.
U.S. Pat. No. 6,660,046 concerns novel pyrazole derivatives as precursors. All exemplary compositions are solvent based and used as a 1-step process for coloring hair.
U.S. Pat. No. 6,638,321 is analogous to U.S. Pat. No. 6,660,046 but with pyrazole precursors replaced by a monobenzene-substituted precursor.
U.S. Pat. No. 6,602,303 concerns oxidative hair coloring compositions containing a cationic polymer in combination with a nonionic surfactant and a hydroxylated solvent. Cationic surfactants are disclosed as optional ingredients.
U.S. Patent Publication No. 2003/0188392 is directed at oxidative hair coloring compositions containing a hydrophobically modified cationic polymer to prevent dripping during use.
U.S. Patent Publication No. 2003/0167579 concerns a ready-to-use oxidation dye composition including substituted paraphenylenediamines.
U.S. Pat. No. 6,660,045 concerns a gel forming hair coloring composition employing specific levels of surfactant, solvent and organic agents to achieve a gel of the correct rheology.
European Patent Specification EP 0137178 concerns dye compositions containing non-oxidative direct nitro dyes in a 1-step coloring process.
European Patent Application EP 1048 290 concerns oxidative dye compositions including certain amphoteric quaternized conditioning polymers to increase dye efficiency.
The present invention seeks improvements over deficiencies in the known art. Among the problems addressed by the instant hair coloring method are increased intensity of color, increased longevity of color, reduced damage of hair, and improved feel of hair after dyeing.